forked from gardener/gardener
-
Notifications
You must be signed in to change notification settings - Fork 0
/
dns.go
122 lines (101 loc) · 3.9 KB
/
dns.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
// Copyright (c) 2018 SAP SE or an SAP affiliate company. All rights reserved. This file is licensed under the Apache Software License, v. 2 except as noted otherwise in the LICENSE file
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package utils
import (
"errors"
"fmt"
"net"
"sort"
"time"
"github.com/miekg/dns"
"github.com/gardener/gardener/pkg/logger"
)
// LookupDNSHost performs a DNS lookup for the given <domain>. In case of success, it will return the list
// of records. If the domain is not resolvable, it will return nil.
func LookupDNSHost(domain string) ([]string, error) {
if net.ParseIP(domain) != nil {
return nil, fmt.Errorf("Detected misuse of domain lookup, an IP was used instead of a domain A record")
}
nsRecords, err := lookUPDNSRecord(domain, dns.TypeA)
if err != nil {
return nil, err
}
sort.Strings(nsRecords)
return nsRecords, nil
}
// LookupDNSHostCNAME performs a CNAME DNS lookup for the given <domain>. In case of success, it will return
// the record. If the domain is not resolvable (or is not of type CNAME), it will return an empty string.
func LookupDNSHostCNAME(domain string) (string, error) {
nsRecords, err := lookUPDNSRecord(domain, dns.TypeCNAME)
if err != nil {
return "", err
}
// A CNAME Query returns a string slice with a length of 1, so we get the CNAME from the slice
return nsRecords[0], nil
}
// dnsQuery initializes the client as well as the message for DNS and initiates the DNS Query
func dnsQuery(queryName string, queryType uint16) (*dns.Msg, error) {
localMessage := &dns.Msg{
MsgHdr: dns.MsgHdr{
RecursionDesired: true,
},
Question: make([]dns.Question, 1),
}
localClient := &dns.Client{
ReadTimeout: 5 * time.Second,
}
conf, err := dns.ClientConfigFromFile("/etc/resolv.conf")
if err != nil || conf == nil {
return nil, fmt.Errorf("config file might be empty, or something went wrong with initiating client: %s", err)
}
localMessage.SetQuestion(queryName, queryType)
for _, server := range conf.Servers {
r, _, err := localClient.Exchange(localMessage, fmt.Sprintf("%s:%s", server, conf.Port))
if err != nil {
return nil, err
}
if r == nil || r.Rcode == dns.RcodeNameError || r.Rcode == dns.RcodeSuccess {
return r, err
}
}
return nil, errors.New("No name server to answer the question")
}
// lookUPDNSRecord filters results from a dnsQuery and returns a slice of valid RR records or error in case of failure
func lookUPDNSRecord(domain string, qtype uint16) ([]string, error) {
if net.ParseIP(domain) != nil {
return nil, fmt.Errorf("Detected misuse of domain lookup, an IP was used instead of a domain CNAME")
}
r, err := dnsQuery(dns.Fqdn(domain), qtype)
if err != nil || r == nil {
return nil, fmt.Errorf("cannot retrieve the list of name servers for %s: %+v", dns.Fqdn(domain), err)
}
if qtype == dns.TypeCNAME && r.Rcode == dns.RcodeNameError {
return nil, fmt.Errorf("no such domain %s", dns.Fqdn(domain))
}
if len(r.Answer) == 0 {
return nil, fmt.Errorf("empty answer query response from server, the lookup type for the records might be incorrect")
}
var recordsToReturn []string
for _, record := range r.Answer {
switch t := record.(type) {
case *dns.A:
recordsToReturn = append(recordsToReturn, t.A.String())
case *dns.CNAME:
recordsToReturn = append(recordsToReturn, t.Target)
default:
logger.Logger.Warn("Invalid answer record received doing nothing")
}
}
return recordsToReturn, nil
}